【leetcode 二叉树 C++】【剑指 Offer】 32 - I. 从上到下打印二叉树

剑指 Offer 32 - I. 从上到下打印二叉树

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<int> levelOrder(TreeNode* root) {  // 层次遍历，默写题
        vector<int> V;
        queue<TreeNode*> Q;
        TreeNode* p;
        if(root) Q.push(root);
        while(!Q.empty()) {
            p = Q.front();
            Q.pop();
            V.push_back(p->val);
            if(p->left) Q.push(p->left);
            if(p->right) Q.push(p->right);
        }
        return V;
    }
};